Method and Device for 3-D Display Based on Random Constructive Interference

ABSTRACT

The present invention relates to a method and an apparatus for 3-D display based on random constructive interference. It produces a number of discrete secondary light sources by using an amplitude-phase-modulator-array, which helps to create 3-D images by means of constructive interference. Next it employs a random-secondary-light-source-generator-array to shift the position of each secondary light source to a random place, eliminating multiple images due to high order diffraction. It could be constructed with low resolution liquid crystal screens to realize large size real-time color 3-D display, which could widely be applied to 3-D computer or TV screens, 3-D human-machine interaction, machine vision, and so on.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/865,809, filed on Aug. 2, 2010, entitled “Method and Devices for 3-DDisplay Based on Random Constructive Interference,” which is a filingunder 35 U.S.C. 371 of International Application No. PCT/CN2009/000112filed Jan. 23, 2009, entitled “Three-Dimensional Displaying Method andApparatus Based on Random Constructive Interference,” which claimspriority to Chinese Application No. 200810046861.8 filed on Feb. 3,2008, which these applications are incorporated by reference herein intheir entirety.

FIELD OF THE INVENTION

The present invention relates to methods and apparatuses for 3-D displayand 3-D photography based on random constructive interference. Theinvention could be used as computer or TV screens, for intelligenthuman-machine interaction and machine vision etc., in such field aseducation, scientific research, entertainment, advertisement and so on.

BACKGROUND OF THE PRESENT DISCLOSURE

Large size real-time 3-D display with wide viewing angle has long beendreamed of. We may classify existing 3-D display techniques roughly intotwo classes, pseudo 3-D display and true 3-D display. In pseudo3D-display various means are employed to present respectively to twoeyes of an observer two pictures being taken at slightly differentangles. The observer combines the two pictures and forms a virtual 3-Dimage in his/her mind. In true 3-D display a real 3-D image is createdin space, like what happens in holographic display. To watch pseudo 3-Ddisplay one has to wear some kind of auxiliary apparatuses likepolarization spectacles, or the eye position of an observer has to betracked, limiting the number of observers to one or a few more. For true3-D display observers need not wear any auxiliary apparatus and couldwatch a displayed 3-D image conveniently as if they watch a real object.

For the past decades with the development of liquid crystal display(LCD), people tried to replace hologram plates with liquid crystalpanels and succeed in real-time holographic 3-D display for very smallobjects. However even for projection type liquid crystal panels thepixel pitch is usually more than ten micrometers, in other words thespace resolution is less than one hundred line pairs per millimeter,which is nearly two orders lower than that of a hologram plate.Therefore the holographic 3-D images generated so far by usingprojection type liquid crystal panels were as small as one centimeter sothat very low density interference patterns were involved. At the sametime the created holographic 3-D images were far away from the liquidcrystal panels, yielding a very narrow viewing angle.

For conventional liquid crystal computer screens the pixel pitchesincrease to about 0.29 mm, which means the resolutions are only severalline pairs per millimeter. It is impossible to generate 3-D holographicimages with such low resolution liquid crystal screens. In addition toproduce a large size holographic 3-D image with wide viewing angle largespace-bandwidth product is necessary. At present, liquid crystal panelscould only provide a space-bandwidth product around 10⁶, several orderslower than what is necessary. To make things worse with the increase ofspace-bandwidth product huge data becomes inevitable, which puts a greatburden on real time data processing.

SUMMARY OF THE PRESENT INVENTION

The first aim of the present invention is to provide a method based onrandom constructive interference for fast and stable large size 3-Ddisplay using two-dimensional display devices with low resolution andrelatively low space-bandwidth product. The second aim of the presentinvention is to provide a method for 3-D photography which is capable ofmeasuring and recording 3-D positions and color information of realobjects, and is widely applicable to human-machine interaction, machinevision, and so on.

The third aim of the present invention is to provide an apparatus forlarge size and wide viewing angle real-time color 3-D display forcomputer and TV screens, which could make use of existing LCD techniqueand could shift between 3-D and 2-D display easily.

For these purposes the present invention provided following solutions.

A 3-D display method based on random constructive interferencecomprising following steps:

A: Decompose a 3-D image into discrete pixels;

B: Pick one of the pixels;

C: Select randomly coherent secondary light sources from a coherentsecondary light source array in which the positions of the secondarylight sources are of a uniform random distribution, the number ofrandomly selected secondary light sources being proportional to theintensity of the pixel picked up in step B;

D: For each coherent secondary light source selected in step C calculateits distance to the pixel picked up in step B and the related phasedifference, and take the phase difference as the phase adjustment thatshould be performed by the coherent secondary light source to generatethe said pixel;

E: For each coherent secondary light source selected in step C set theamplitude adjustment it should make to generate the pixel picked up instep B as a constant or proportional to the intensity of the pixel;

F: For each discrete pixel obtained in step A, repeat step B throughstep E, record the amplitude and phase adjustment that should be made byeach coherent secondary light source for each discrete pixel; for eachcoherent secondary light source, in way of complex-amplitude addition,sum up all the recorded amplitude and phase adjustment it should make togenerate the said pixels, and take the amplitude and phase of resultingcomplex amplitude as the total amplitude and phase adjustment it shouldmake;

G: For each coherent secondary light source calculate its final phaseadjustment by subtracting its primary phase from the total phaseadjustment determined in step F and use the total amplitude adjustmentdetermined in step F as its final amplitude adjustment; let eachcoherent secondary light source with random position distributionproduce the final phase and amplitude adjustment.

A method for 3-D photography based on random constructive interference,comprising following steps:

A: Following the 3-D display method based on random constructiveinterference, generate light spots in 3-D space using a coherentsecondary light source array in which the positions of secondary lightsources are of a uniform random distribution.

B: Focus a conventional camera on the position of the light spotsgenerated in step A and record an image;

C: Repeat step A through step B so that the light spots generated instep A scan through a 3-D space, meanwhile analyze the images taken instep B; the positions of the light spots represent the local 3-Dcoordinates of the surface when their image sizes become minima;meanwhile the color and brightness of the surface of the object beingthe same as recorded by the conventional camera.

A 3-D display device based on random constructive interferencecomprising: a coherent light source that emits coherent light; anilluminating optic system disposed to receive the coherent light andemit an expand coherent light beam; an amplitude-phase-modulator-arraydisposed to receive the expand coherent light beam and to produce asecondary light source array; arandom-secondary-light-source-generator-array disposed and aligned withthe amplitude-phase-modulator-array so that onerandom-secondary-light-source-generator receives the light from oneamplitude-phase-modulator in the amplitude-phase-modulator-array andcreates a new coherent secondary light source array in which thepositions of the secondary light sources are of a uniform randomdistribution.

The said amplitude-phase-modulator-array comprising: the first polarizerdisposed to receive the expanded light beam from illuminating opticsystem and to emit a polarized light beam; the first beam splitterdisposed to receive the polarized light beam and to split it into twoequal light beams; two reflectors disposed to receive the two equallight beams and reflect them normally onto two transmission liquidcrystal panels respectively; two transmission liquid crystal panelstogether with the second beam splitter disposed to form a Michelsoninterferometer with one transmission liquid crystal panel placed at anangle of 45 degree to the second beam splitter'shalf-reflect-half-transmit surface and in mirror symmetry with anothertransmission liquid crystal panel relative to the second beam splitter'shalf-reflect-half-transmit surface; the second beam splitter disposed toreceive the light beams modulated by two transmission liquid crystalpanels and combine them to form an integrated light beam; the secondpolarizer disposed in parallel with one of the two liquid crystal panelsto receive normally the integrated light beam formed by the second beamsplitter, the polarization directions of the first and the secondpolarizer being arranged to set the two transmission liquid crystalpanels in phase-mostly mode; a projection lens disposed to receive thepolarized light emitted from the second polarizer and form a magnifiedreal image of the two transmission liquid crystal panels.

The said random-secondary-light-source-generator-array being disposed atthe image plane of the liquid crystal panels generated by the projectionlens and comprising: a transparent scattering screen or a reflectivescattering screen or a micro-lens-array disposed by or fabricated on atransparent plate covered with an opaque film bearing transparentmicro-holes whose positions are of a uniform random distribution, thediameter of each micro-hole being smaller than the size of the images ofthe pixels of the liquid crystal panels, each micro-lens in themicro-lens-array being aligned with each micro-hole on the opaque filmso that the optic axis of each micro-lens passes the center of themicro-hole it aligned with.

The said illuminating optic system comprising: two convex lenses withdifferent focal lengths, the convex lens with smaller focal length beingdisposed to receive the light, the convex lens with larger focal lengthbeing disposed with its object focus at the image focus of the convexlens with smaller focal length to form a telescope and to emit anexpanded light beam.

The said amplitude-phase-modulator-array comprising: the first polarizerdisposed to receive the expanded light beam from illuminating opticsystem and to emit a polarized light beam; a beam splitter disposed toreceive the polarized light beam and to split it into two equal lightbeams; two reflective liquid crystal panels or liquid crystal lightvalves disposed to receive normally the two equal light beamsrespectively and reflect them back, the reflective liquid crystal panelsor liquid crystal light valves together with the beam splitter disposedto form a reflective Michelson interferometer with one reflective liquidcrystal panel or one liquid crystal light valve placed at an angle of 45degree to the beam splitter's half-reflect-half-transmit surface and inmirror symmetry with another reflective liquid crystal panel or liquidcrystal light valve relative to the beam splitter'shalf-reflect-half-transmit surface, the beam splitter being disposedalso to receive the light beams modulated by the reflective liquidcrystal panels or liquid crystal light valves and combine them to forman integrated light beam; the second polarizer disposed in parallel withone of the two reflective liquid crystal panels or liquid crystal lightvalves to receive normally the integrated light beam formed by the beamsplitter, the polarization directions of the first and the secondpolarizer being arranged to set two reflective liquid crystal panels orliquid crystal light valves in phase-mostly mode; an projection lensdisposed to receive the polarized light emitted from the secondpolarizer and form a magnified real image of two reflective liquidcrystal panels or liquid crystal light valves; twodigital-mirror-devices disposed behind two liquid crystal light valvesto project two optic images onto the back of two liquid crystal lightvalves respectively, the optic image projected onto the back of oneliquid crystal light valve being in mirror symmetry with the optic imageprojected onto the back of another liquid crystal light valve relativeto the beam splitter's half-reflect-half-transmit surface.

The said amplitude-phase-modulator-array comprising: a beam splitterdisposed to receive the expanded light beam from illuminating opticsystem and to split it into two equal light beams; twooptically-addressed-electro-optic-phase-modulators disposed to receivenormally the two equal light beams with their electro-optic materialfilms and reflect them back, twooptically-addressed-electro-optic-phase-modulators together with thebeam splitter disposed to form a reflective Michelson interferometerwith one optically-addressed-electro-optic-phase-modulator placed at anangle of 45 degree to the beam splitter's half-reflect-half-transmitsurface and in mirror symmetry with anotheroptically-addressed-electro-optic-phase-modulator relative to the beamsplitter's half-reflect-half-transmit surface, the beam splitter beingdisposed also to combine the light beams reflected and modulated by twooptically-addressed-electro-optic-phase-modulators to form an integratedlight beam; an optic lens disposed to receive the integrated light beamand form a magnified real image of twooptically-addressed-electro-optic-phase-modulators; twodigital-mirror-devices disposed behind twooptically-addressed-electro-optic-phase-modulators to project two opticimages onto the optic-sensitive films on the back of twooptically-addressed-electro-optic-phase-modulators respectively, theoptic image projected onto the back of oneoptically-addressed-electro-optic-phase-modulator being in mirrorsymmetry with the optic image projected onto the back of anotheroptically-addressed-electro-optic-phase-modulator relative to the beamsplitter's half-reflect-half-transmit surface.

The said optically-addressed-electro-optic-phase-modulator comprising:the first film of optic-sensitive material, the second film of opaquematerial, the third reflective film and the forth film of electro-opticmaterial, all of them being sandwiched between two transparentconductive glasses in the given order.

The said random-secondary-light-source-generator-array comprising: twoidentical opaque plates bearing transparent micro-holes whose positionsare of a uniform random distribution disposed at the object plane of theprojection lens, one opaque plate being placed at an angle of 45 degreeto the beam splitter's half-reflect-half-transmit surface and in mirrorsymmetry with another opaque plate relative to the beam splitter'shalf-reflect-half-transmit surface.

The said amplitude-phase-modulator-array comprising: the firstpolarizer; the first transmission liquid crystal panel disposed by thefirst polarizer; the second polarizer disposed by the first transmissionliquid crystal panel; the second transmission liquid crystal paneldisposed by the second polarizer; the third polarizer disposed by thesecond transmission liquid crystal panel, the pixels on the firsttransmission liquid crystal panel being aligned with the pixels on thesecond transmission liquid crystal panel, the polarization directions ofthe three polarizer being arranged to set one transmission liquidcrystal panel in phase-mostly mode and another transmission liquidcrystal panel in amplitude-mostly mode.

Position of pixels on the said two transmitted or reflective liquidcrystal panels are of an identical uniform random distribution.

The said random-secondary-light-source-generator-array comprising: thefirst micro-lens-array on which the micro-lens are of a periodicaldistribution; the second micro-lens-array on which the micro-lens are ofa uniform random distribution being disposed in parallel with the firstmicro-lens-array and aligned with the first micro-lens-array so that thefocused light emitted from each micro-lens of the first micro-lens-arrayilluminates one micro-lens of the second micro-lens-array and the imagefocus of each micro-lens of the first micro-lens-array falls within onefocal length of one micro-lens of the second micro-lens-array.

The said random-secondary-light-source-generator-array comprising: abundle of optically isolated single-mode fibers fabricated so that thesingle-mode fibers within the bundle are glue together and polished atthe first end and the spaces between adjacent single-mode fibers are ofa random distribution at the second end; a micro-lens-array disposed tofocus the light into the cores of the single-mode fibers within thebundle at the first end, one micro-lens in the micro-lens-array beingaligned with one single-mode fiber.

The present invention is based on the following two facts. Firstly, alight spot, or a 3-D pixel, could be generated in free space byconstructive interference of a number of coherent discrete secondarylight sources. Lots of 3-D pixels make up a 3-D image. Secondly, if thepositions of above coherent discrete secondary light sources arerandomly located, high order diffraction could be greatly depressed sothat only one 3-D image is created. Detailed explanation is given asfollows.

Suppose N discrete secondary light sources are fixed on the X-Y plane,whose amplitude and phases are adjustable. For convenience of analysis,we further suppose the discrete secondary light sources are point lightsources. They emit spherical light waves polarized along Y axis. Thenthe complex amplitude of the optic field at any position r_(m) is asummation of the N spherical waves emitted by these N secondary pointlight sources and the resulting electric field component along Y axiscould be described as,

$\begin{matrix}{{U\left( r_{m} \right)} = {\sum\limits_{j = 1}^{j = N}{\frac{A_{0\; j}A_{{c\; j},m}{\cos \left( \theta_{j,m} \right)}{\exp \left\lbrack {\left( {\Phi_{{cj},m} + \Phi_{0\; j}} \right)} \right\rbrack}}{{r_{m} - R_{j}}}{\exp \left\lbrack {{- }\; k_{j,m}\mspace{14mu} \bullet \mspace{14mu} \left( {r_{m} - R_{j}} \right)} \right\rbrack}}}} & (1)\end{matrix}$

where vector R_(j), j=1, 2, . . . N stands for the coordinates of Nsecondary point light sources, k_(j,m) for the wave vector of the lightemitted from the j^(th) secondary point light source towards r_(m),θ_(j,m) for the angle between Y axis and the electric component of thelight field emitted from the j^(th) secondary point light source towardsr_(m), θ_(j,m)<90°, A_(0j) and Φ_(0j) for primary amplitude and phase ofthe j^(th) secondary light source respectively. A_(0j) depends on theintensity of j^(th) secondary point light source and is also a functionof direction. A_(cj,m) and Φ_(cj,m) stand for additional amplitude andphase adjustment made by the j^(th) secondary light source underelectrical control. Both A_(0j) and A_(cj,m) are positive. To ensureconstructive interference at position r_(m) it is necessary to digitallyset the phase Φ_(cj,m) of each secondary point light source so that,

Φ_(cj,m)+Φ_(0j) −k _(j,m)·(r _(m) −R _(j))=2nπ  (2)

Where n is an integer. When Eq. (2) is satisfied, Eq. (1) becomes,

$\begin{matrix}{{U\left( r_{m} \right)} = {\sum\limits_{j = 1}^{j = N}\frac{A_{0\; j}A_{{cj},m}{\cos \left( \theta_{j,m} \right)}}{{r_{m} - R_{j}}}}} & (3)\end{matrix}$

Therefore the light field at position r_(m) reaches a maximum, creatinga light spot, or a 3-D pixel, in free space. The larger the number N is,the brighter and sharper the 3-D pixel is. Away from the position ofr_(m), the intensity of the light field decreases dramatically.

From Eq. (3) it could be seen that the intensities of the generated 3-Dpixels depend on both the number N and the amplitude A_(cj,m) of thesecondary point light sources. When both N and A_(cj,m) keep constant,according to Eq. (3), the intensity of a 3-D pixel is roughly in inverseproportion to the square of |r_(m)−R_(j)|. That means the larger thedistance |r_(m)−R_(j)| of the generated 3-D pixel from secondary pointlight sources is, the lower the intensity is. Since an observer standsat opposite side and faces the secondary point light sources, above factimplies that the closer the generated 3-D pixel towards the observer,the lower its intensity. However it should be noticed that the intensitycalculated by Eq. (3) does not precisely represent the brightness of thegenerated 3-D pixel seen by the observer since not all the light emittedby N secondary point light sources could come into the eyes of anobserver. To estimate how many lights could enter the eye of anobserver, we may draw a cone taking observer's pupil as the bottom andthe 3-D pixel as the apex and stretch the cone in opposite directiontowards the secondary point light sources. It is easy to see that onlythe light emitted by the secondary light sources located within the conecould reach the pupil of the observer and contribute to the brightnessof the 3-D pixel. Suppose the distance between the generated 3-D pixeland the observer is d, it could be find from their geometrical relationthat the number N_(eff) of the secondary point light sources locatedwithin the cone is in inverse proportion to the square of d and inproportion to the square of |r_(m)−R_(j)|. Replace N with N_(eff) in Eq.(3), one could find that now the brightness of the generated 3-D pixelseen by the observer is roughly in inverse proportion to the square ofd. In other words, the closer the 3-D pixel towards the observer, thebrighter it appeared to the observer, which is in good agreement withour common sense. Furthermore, A_(cj,m) could be adjusted to compensatefor the influence of the primary amplitude A_(0j) and the angle θ_(j,m)on the intensity of the generated 3-D pixel, so that it appears with thesame intensity when looked from different angle.

It could be seem from Eq. (1) that such a 3-D display system is a linearsystem. Therefore a number of 3-D pixels could be created in free spaceto form a discrete 3-D image. Following above method we may indeed carryout 3-D display by utilizing each pixel of a 2-D liquid crystal screenas a discrete secondary light source. However there exists a seriousproblem. Along the directions of ±1, ±2 . . . order diffractions,multiple images would be generated at the same time due to periodicalarrangement of the pixels. Near the screen these images overlap witheach other, decreasing the image quality. Away from the screen theimages make a small angle with the screen yielding a very narrow viewingangle, although they are separated from each other.

To avoid the creation of multiple images, present invention let thediscrete secondary light sources locate at random positions. The imagesat ±1, ±2 . . . order diffraction directions disappear due to the lossof the periodicity of the positions of the secondary light sources andonly one 3-D image is formed. Near the screen the image makes a verylarge angle with the screen yielding a very wide viewing angle.

When coherent secondary point light sources with random distribution areemployed, it could be revealed using Eq. (1) that a single 3-D pixelmight be created at position r_(m). If a total of M discrete 3-D pixelsneed be created, denote the amplitude and phase adjustment made by thej^(th) secondary light point source to create the m^(th) 3-D pixel asA_(cj,m) and Φ_(cj,m), the total complex amplitude adjustment thatshould be carried out by j^(th) secondary light source should be,

$\begin{matrix}{A_{j} = {\sum\limits_{m = 1}^{m = M}{A_{{cj},m}{\exp \left( \Phi_{{cj},m} \right)}}}} & (4)\end{matrix}$

According to Eq. (1-4), Eq. (1) reaches maxima when and only whenr=r_(m), m=1, 2, . . . M, since at these locations Eq. (2) is satisfied.All the 3-D pixels generated as such make up a 3-D image.

From the simulation based on Eq. (1), (2) and (4) it was found thatmultiple 3-D images were indeed inevitable when periodic secondary lightsources were used. However, when the secondary point light sources shiftrandomly within a certain range around their initial periodic positions,high order diffraction images disappear gradually as the range of shiftbecomes large. When the range of shift reaches 90% of the initial periodhigh order diffraction images disappear completely and only a zero order3-D image remains. For uniform random distribution a secondary lightsource has the same probability to locate at any position and theperiodicity could be destroyed completely. Other type of randomdistribution could also be adopted if high order diffraction imagescould be depressed.

In above analyses the secondary light sources are assumed to be pointlight sources. For secondary light sources with a certain size the sameconclusion could be reached although the calculation becomes morecomplicated since the contribution of each secondary light source needbe calculated by integration. It is also worth to point out that above3-D display method is very robust. For example, if a small fraction ofsecondary light sources go wrong, the intensity of generated 3-D pixelswould change only slightly. This is due to the fact that each 3-D pixelbeing a result of constructive interference of hundreds and thousands ofsecondary light sources. If Eq. (2) was not strictly satisfied, that is,the phase difference between two light waves arriving at a givenposition was not exactly multiple of 2π, but with an error less thanπ/2, the intensity of resulting light field still become larger thanindividual light field. Of course the maxima are reached only when Eq.(2) is strictly satisfied. In a word, the intensity of created 3-Dpixels might change slightly due to a small decrease of the number ofsecondary light sources, or small errors in carrying out phase andamplitude adjustment. However the position and the number of pixels ofcreated 3-D images would not change. In contrast when a pixel in a 2-Dscreen goes wrong it become inaccessible forever, making the displayedscene incomplete.

A 3-D display device based on above principle comprises mainly fourcomponents, namely, an amplitude-phase-modulator-array, arandom-secondary-light-source-generator-array, a coherent light sourceand an illuminating optic system. Detailed description is given below.

The amplitude-phase-modulator-array is responsible for producingdiscrete secondary light sources and carrying out independent amplitudeand phase modulation for each secondary light source. Anamplitude-phase-modulator-array might be constructed using liquidcrystal panels. Each pixel of a liquid crystal panel acts as a secondarylight source. It is known that for a single SN or other type liquidcrystal panel, the amplitude adjustment and phase adjustment are usuallycorrelated with each other. However, if the polarizer on its two sidesare set to proper polarization directions a single liquid crystal panelmight work in phase-mostly mode or amplitude-mostly mode. Based on thisfact, simultaneous independent amplitude and phase modulation might beperformed by a combination of two liquid crystal panels. One way tocombine two liquid crystal panels is to place them in an order so thatthe illuminating light passing them in sequence. The total modulation isa vector production of the modulations made by each liquid crystalpanel. Another way to combine two liquid crystal panels is to place themon the two arms of a Michelson interferometer so that the illuminatinglight passing them respectively and then combine together. The totalmodulation is a vector addition of the modulations made by each liquidcrystal panel. Which way should be adopted depends on what type and whatsize of liquid crystal panels are used. Besides liquid crystal panels,there are also other devices to create discrete secondary light sources.For example, optically-addressed-electro-optic-phase-modulators proposedby present invention might be utilized for the purpose.

The random-secondary-light-source-generator-array is responsible fortransforming the discrete secondary light sources produced byamplitude-phase-modulator-array into new secondary light sources whosepositions are of a random distribution. There are various ways to createrandomly located secondary light sources. A direct way is to randomlyarrange the pixels when designing a liquid crystal panel. In this case,no additional random-secondary-light-source-generator-array isnecessary, or the liquid crystal panel itself is a combination of anamplitude-phase-modulator-array and arandom-secondary-light-source-generator-array. For existing commercialliquid crystal panels, additionalrandom-secondary-light-source-generator-arrays have to be employed sincetheir pixels are periodically arranged. Arandom-secondary-light-source-generator-array may be built with anopaque plate bearing a number of transparent holes whose positions arerandomly located, or with a micro-lens-array in which the positions ofthe micro-lenses are randomly located, or with a micro-prism array inwhich the directions of the micro-prisms are randomly arranged, or acombination of them. A random-secondary-light-source-generator-array mayalso be built in other ways, for example by means of a bundle of fibersas proposed by present invention.

As a coherent imaging system, a 3-D display device based on randomconstructive interference needs a coherent laser, whose coherent lengthshould be larger than the possible maximum optic path difference betweenany two secondary light sources to any 3-D pixel. The brightness andcontrast of a 3-D image depends on the power of the laser. In order todisplay color 3-D images, lasers with different wavelengths should alsobe employed. When black and white liquid crystal panels are used, lasersfor basic colors may be turned on and off in sequence to display color3-D images based on persistence of vision. When color liquid crystalpanels are used, all the basic colors may be turned on at the same time.Pixels covered with different color filters perform amplitude-phasemodulations for different wavelengths. Therefore all the basic colorimages could be created at the same position and make up a true 3-Dcolor image. For 3-D measurement and human-machine interaction, nearinfrared lasers might be used to avoid disturbances to the observer.Since the diameter of a primary laser beam is usually very small, anoptic illuminating system is necessary to expand the laser beam. Anoptic illuminating system should also be thin and light for portabledevices.

To improve the quality of 3-D images generated by above 3-D displaydevices based on random constructive interference, some auxiliary opticelements may be used. For example, a Fresnel lens may be employed tomagnify a 3-D image and separate the image away from the brightsecondary light sources to avoid the interference of background light tothe observer.

If above 3-D display device stops amplitude and phase modulationfollowing above random constructive interference principle, and changesmainly the intensities of secondary light sources by amplitude, 2-Dimages could then be displayed. In other words, a 3-D image device basedon random constructive interference may shift freely between a 3-Ddisplay device and a 2-D display device under the control of software.

With the aid of a conventional camera, above 3-D display method couldalso be used to take 3-D images and carry out 3-D measurements. To do soone may display an array of light spots or lines in free space and letthem scan in space repeatedly, meanwhile monitor where the light spotsor lines touch the surface of an object with a conventional camera. Thepre-known positions of the light spots or lines help to determine thecoordinates of the surface of an object. Furthermore the movingdirection and speed of the object could be calculated. Similarly, if wedisplay a 3-D button in space and monitor when a finger touches thebutton, 3-D human machine interaction could be performed.

Present invention has following advantages compared with existingtechniques:

Firstly, true 3-D images are displayed in free space. Observers maywatch the image as if watching a real object without bearing anyauxiliary apparatus. There is no need to track the eye position of anobserver. Many observers may watch the image at the same time and changetheir positions as they like. Secondly, large size real-time color 3-Dimages could be created with wide viewing angle. Thirdly, since it isbased on a principle totally different from traditional holography, noreference light is necessary and there is also no need to record highdensity interference patterns. As a result, it does not require densesecondary light sources and existing LCD techniques could be used.Fourthly, it is very robust. The intensity of created 3-D pixels mightchange slightly due to small decrease of the number of secondary lightsources, or small errors in carrying out phase and amplitude adjustment.However, the positions and the number of created 3-D pixels would notchange. Fifthly, it could easily shift between 2-D display and 3-Ddisplay under the control of software without any hardware change.Sixthly, it could carry out 3-D measurement and 3-D human machineinteraction when cooperated with a conventional camera.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of present inventionusing two small-size TFT-ST projection type liquid crystal panels.

FIG. 2 is a schematic diagram of an embodiment ofrandom-secondary-light-source-generator-array using an opaque platebearing holes whose positions are of a random distribution.

FIG. 3 is a schematic diagram of an embodiment of present inventionusing two reflective liquid crystal panels.

FIG. 4 is a schematic diagram of an embodiment of present inventionusing two liquid crystal light valves.

FIG. 5 is a schematic diagram of an embodiment of present inventionusing two optically-addressed-electro-optic-phase-modulators.

FIG. 6 is a schematic diagram of anoptically-addressed-electro-optic-phase-modulator.

FIG. 7 is a schematic diagram of an embodiment of present inventionusing two large-size TFT-ST liquid crystal panels.

FIG. 8 is a schematic diagram of an embodiment ofrandom-secondary-light-source-generator-array using twomicro-lens-arrays.

FIG. 9 is a schematic diagram of an embodiment ofrandom-secondary-light-source-generator-array using a bundle ofsingle-mode fibers.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a 3-D display device based on randomconstructive interference using two small-sized TFT-ST projection typeliquid crystal panels. It comprises an amplitude-phase-modulator-array1, a random-secondary-light-source-generator-array 2, a coherent lightsource 3 and an illuminating optic system 4. Theamplitude-phase-modulator-array comprises two transmission liquidcrystal panels 5,6, two polarizer 7, 8, two beam splitters 9, 10, tworeflectors 11,12 and a projection lens 13. Two beam splitters 9,10 andtwo reflectors 11,12 are disposed to form a Michelson interferometerwith two transmission liquid crystal panels 5,6 placed on theinterferometer's two arms respectively. The first transmission liquidcrystal panels 5 seats at an angle of 45 degree tohalf-reflect-half-transmit surface A1-A2 of the second beam splitter 9and in mirror symmetry with the second transmission liquid crystal panel6 relative to the second beam splitter 9's half-reflect-half-transmitsurface A1-A2. Both transmission liquid crystal panels 5 and 6 are at adistance of one to two focal lengths away from the projection lens 13.The first polarizer 7 is placed at the entrance port of the Michelsoninterferometer to receive light and in parallel with the secondtransmission liquid crystal panel 6. The second polarizer 8 is placed atthe exit port of the Michelson interferometer and in parallel with thefirst transmission liquid crystal panel 5. The polarization directionsof the first and the second polarizer 7,8 are arranged to set the twotransmission liquid crystal panels 5,6 in phase-mostly mode, to do sothe polarization direction of polarizer 7 is rotated at an angle of 45degree with the polarization direction of polarizer 8 (differentpolarization direction may be required for different type of liquidcrystal panels).

The illuminating optic system 4 comprises the first optic lens 16 withsmaller focal length disposed to receive the light; the second opticlens 17 with larger focal length disposed with its object focus at theimage focus of the first optic lens 16 to form a telescope and to emitan expanded light beam. If a compact illuminating optic system isrequired, the first convex optic lenses 16 may be replaced by a concaveoptic lens with its object focus placed at the second optic lens 17'sobject focus. The parallel laser beam emitted from coherent light source3 is first focused by the first optic lens 16 and transformed intoparallel laser beam again but with larger diameter by the second opticlens 17. The expanded laser beam penetrates normally the first polarizer7 and gets split by the first beam splitter 10 into two equal beams.After being reflected by two reflectors 11 and 12, the two equal beamspenetrate normally the two transmission liquid crystal panels 5 and 6respectively and get combined by the second beam splitter 9 to form anintegrated laser beam. The integrated laser beam penetrates normally thesecond polarizer 8 and gets projected by the projection lens 13. Sincethe pixels on both transmission liquid crystal panels 5 and 6 arealigned accurately with each other and within a range of one to twofocal lengths from the projection lens 13, they form enlarged realimages on opaque plate 14, which bears quantities of transparentmicro-holes. These overlapped images produce a secondary light sourcearray with variable amplitude and phase in way of vector addition.

The random-secondary-light-source-generator-array 2 in FIG. 1 comprisesa micro-lens-array 15 fabricated on an opaque plate 14 bearingtransparent micro-holes that are of a uniform random distribution. Eachmicro-lens in the micro-lens-array 15 is aligned with each micro-hole onthe opaque plate 14 so that the optic axis of each micro-lens 15 passesthe center of the micro-hole it aligned with. As illustrated in FIG. 2,opaque plate 14 is made by covering a transparent plate with an opaquefilm. The transparent micro-holes are produced by etching through theopaque film, one micro-hole for one pixel of the transmission liquidcrystal panel 5 or 6. The diameter of each micro-hole is made smallerthan the size of the image of the pixels of the transmission liquidcrystal panels 5 or 6 (as illustrated by broken line) so that amicro-hole could move around within a certain range. The smaller thediameter of each micro-hole is, the larger the range of free movementand the larger the optic energy loss. Although the pixels oftransmission liquid crystal panel 5 or 6 and their image on opaque plate14 are of a periodic distribution, the new secondary light sourcesgenerated by micro-lens-array 15 are of a random distribution. This isbecause the micro-holes on opaque plate 14 are of a random distribution.The advantage to form a coherent secondary light source array byprojection is that it may cover a large area which is essential forcreation of large size 3-D images.

As could be seen in FIG. 1, there is an auxiliary optic element, theFresnel lens 19, placed in front opaque plate 14. Its function is totransform divergent light into parallel light before it's incidence onopaque plate 14. As a result the focused new secondary light sources bymicro-lens 15 emit symmetric divergent light, providing a better 3-Dimage quality for observers seating right before the device. WithoutFresnel lens 19 the secondary light sources would emit asymmetricdivergent light, making the 3-D image appears darker for observersseating right before the device and brighter for observers seating at alarge angle with the device. Any way Fresnel lens 19 has a limitedauxiliary function to improve image quality. In addition, the entranceand exit surfaces of beam splitter 9,10 and other related surfaces thatmay cause reflection may be evaporated with a thin anti-reflection filmto depress the interference of reflected light.

Referring to the device illustrated in FIG. 1, the 3-D display methodbased on random constructive interference put forth by present inventionmay be carried out as follows. It comprises seven steps:

A: Decompose a 3-D image 18 to be displayed into M discrete pixels;

B: Pick up one pixel m from the pixels obtained in step A;

C: Select randomly N coherent secondary light sources from a coherentsecondary light source array in which the positions of the secondarylight sources are of a uniform random distribution, the number N dependson the intensity of the pixel m picked up in step B; The higher theintensity is, the larger the number N is;

D: For each coherent secondary light source j selected in step C,calculate its distance to the pixel m picked up in step B and therelated phase difference Φ_(cj,m)=k_(j,m)·(r_(m)−R_(j)), and take thephase difference Φ_(cj,m) as the phase adjustment that should beperformed by the coherent secondary light source j to generate the saidpixel m;

E: For each coherent secondary light source j selected in step C, setthe amplitude adjustment A_(cj,m) it should be made as a constant orproportional to the intensity of the pixel m picked up in step B;

F: For all the M discrete pixels in step A, repeat step B through stepE, record the amplitude and phase adjustment Φ_(cj,m) A_(cj,m), thatshould be made by each coherent secondary light source j for eachdiscrete pixel m; for each coherent secondary light source j, in way ofcomplex-amplitude addition, sum up all the recorded amplitude A_(cj,m)and phase adjustment Φ_(cj,m),

$A_{j} = {{\sum\limits_{m = 1}^{m = M}{A_{{cj},m}{\exp \left( \Phi_{{cj},m} \right)}}} = {A_{cj}{\exp \left( \Phi_{cj} \right)}}}$

and take the amplitude and phase A_(cj), Φ_(cj) of resulting complexamplitude as the total amplitude and phase adjustment it should make.

G: For each coherent secondary light source j, calculate its final phaseadjustment by subtracting its primary phase Φ_(0j) from the total phaseadjustment Φ_(cj) determined in step F. Of course multiples of 2π phaseadjustment should be cut off. Meanwhile use the total amplitudeadjustment A_(cj) determined in step F as its final amplitudeadjustment. Or divide the total amplitude adjustment A_(cj) determinedin step F by the primary amplitude A_(0j) of coherent secondary lightsource j and multiply the result with a constant c₁, then usec₁A_(cj)/A_(0j) as the final amplitude adjustment to compensate for theprimary amplitude A_(0j) of coherent secondary light source j so thatthe contribution of every secondary light source become equal. Lastlydrive the transmission liquid crystal panels 5 and 6 to make eachcoherent secondary light source j produce above final phase andamplitude adjustment.

According to the principle of coherent interference as represented byEq. (1-4), a primary 3-D image 18 might be created following steps Athrough G. There is only one 3-D image 18 generated because thepositions of secondary light sources are of a random distribution.

In FIG. 1, suppose the transmission liquid crystal panels 5 and 6 eachcontains a total of 1920×1080 pixels and the amplitude adjustmentA_(cj,m)=1 in step E for each secondary light source in creation of one3-D pixel. 3-D pixels with 256 gray levels might be created by changingthe number N of randomly selected coherent secondary light sources instep C. Suppose we chose N=400 for the darkest 3-D pixel. When Nincreases by 16 times to reach N=6400, the intensity of the 3-D pixelwould increase by 256 times. For average intensity we have N≈4800. Thatmeans roughly 1920×1080/4800=432 groups of pixels might be randomlyselected from a total of 920×1080 pixels. If transmission liquid crystalpanels 5,6 are driving with 8-bit D/As, or the maximum gray level ofeach pixel, also maximum value of A_(cj,m) is 256, then each group ofpixels could create about 256 3-D pixels and a total of about 432×256discrete 3-D pixels might be generated. The absolute intensity of each3-D pixel depends on the power of the laser. Very bright 3-D images maybe created using high power lasers. From above estimation it could beseen that 10⁶ 3-D pixels might be generated with a spacebandwidth-product of about 10⁷˜10⁸.

To display an extremely large 3-D scene, several 3-D display devicesbased on random constructive interference as illustrated in FIG. 1 mightbe incorporated, each creating a small part of the scene. The interfacesbetween each part might be made indistinguishable since they aredisplayed in free space away from the device.

In cooperation with a conventional camera, the device illustrated inFIG. 1 might be employed to take 3-D images and carry out 3-Dmeasurement following the steps given below.

A: Following the 3-D display method based on random constructiveinterference, display light spots in 3-D space using a random coherentsecondary light source array produced by a device as illustrated in FIG.1;

B: Focus a conventional camera at the position of the light spotsgenerated in step A and record an image;

C: Repeat step A through step B so that the light spots generated instep A scan through a 3-D space, meanwhile analyze the recorded imagesin step B; the positions of the light spots represent the local 3-Dcoordinates of the surface when their image sizes become minima;meanwhile the color and brightness of the surface of the object beingthe same as recorded by the conventional camera.

3-D coordinates of the entire surface of an object could be determinedfollowing above steps A-C. If large scan steps are adopted in scanning3-D space in step A, very fast 3-D measurement speed might be achieved,while an high accuracy might be obtained if very small scan steps areadopted. If large scan steps are adopted away from the surface of anobject and small scan steps are adopted near the surface by using theknown information from previous scan, then both high accuracy and highspeed could be attained. Above real-time 3-D measurement method mightwidely be applied to 3-D human-machine interaction and machine vision.

FIG. 3 is a schematic diagram of a 3-D display device based on randomconstructive interference using two reflective liquid crystal panels. Itcomprises an amplitude-phase-modulator-array 1, arandom-secondary-light-source-generator-array 2, a coherent light source3 and an illuminating optic system 4. Theamplitude-phase-modulator-array 1 comprises a splitter 9, two polarizer7, 8, a projection lens 13 and two reflective liquid crystal panels,namely liquid crystal on silicon (LCOS) 20,21. Two LCOS 20,21 togetherwith the beam splitter 9 are disposed to form a reflective Michelsoninterferometer with two LCOS 20,21 at its two arms acting as thereflectors. The first reflective liquid crystal panel 20 is placed at anangle of 45 degree to beam splitter 9's half-reflect-half-transmitsurface A1-A2 and in mirror symmetry with the second reflective liquidcrystal panel 21 relative to beam splitter 9'shalf-reflect-half-transmit surface A1-A2. The device illustrated in FIG.3 works in a similar way as the device in FIG. 1. The first polarizer 7is placed at the entrance port of the reflective Michelsoninterferometer to receive light and in parallel with the firstreflective liquid crystal panel 20. The second polarizer 8 is placed atthe exit port of the reflective Michelson interferometer and in parallelwith the second reflective liquid crystal panel 21. The polarizationdirections of the first and the second polarizer 7,8 are arranged to setthe two reflective liquid crystal panel 20 and 21 in phase-mostly mode,to do so the polarization direction of polarizer 7 is rotated at anangle of 45 degree with the polarization direction of polarizer 8(different polarization direction may be required for different type ofreflective liquid crystal panels). The expanded laser beam emitted fromilluminating optical system 4 penetrates normally the first polarizer 7,becomes polarized laser beam and gets split by the beam splitter 9 intotwo equal beams. The two equal beams incident normally on the liquidcrystal layers of the two reflective liquid crystal panels 20 and 21respectively. After reflection the two equal beams get combined by thesame beam splitter 9 to form an integrated laser beam. The integratedlaser beam penetrates normally the second polarizer 8 and gets projectedby the projection lens 13. Since the pixels on both reflective liquidcrystal panels 20 and 21 are aligned accurately with each other andwithin a range of one to two focal lengths from the projection lens 13,they form enlarged real images on opaque plate 14, which bearsquantities of transparent micro-holes. These overlapped images produce asecondary light source array with variable amplitude and phase in way ofvector addition. Next the secondary light source array is transformedinto a new secondary light source array with uniform random distributionby random-secondary-light-source-generator-array 2, which is made upwith a transparent scattering screen 22 covered with an opaque plate 14bearing micro-holes of uniform random distribution. The function oftransparent scattering screen 22 is to make the light emitted bysecondary light sources diverge greatly so that each discrete 3-D pixelis built up with lights coming from a wide range of direction andtherefore could be seen from a wide range of direction, providing a wideviewing angle. The roughness of scattering screen 22 should becontrolled within a proper range so that the phase difference of lightscoming from different parts of the same secondary light source is verysmall. Otherwise they would cancel with each other, lowering theintensity of created 3-D pixels.

FIG. 4 is a schematic diagram of a 3-D display device based on randomconstructive interference using two liquid crystal light valves. Itadopted the same optic configuration as illustrated in FIG. 3 exceptthat two LCOS 20, 21 are now replaced by two liquid crystal light valves23, 24 together with two digital light processors (DLP) 26. A DLP 26comprises a light source 27, a digital micro-mirror-device 28 and anoptic lens 29. The light emitted from light source 27 is reflected bydigital micro-mirror-device 28 and projected onto the back of liquidcrystal light valve 23 or 24 by optic lens 29 to form an image withspecific intensity distribution. If only one DLP is used, a color filteris necessary to project images with different colors onto the back ofliquid crystal light valves 23 and 24 respectively.

A liquid crystal light valve comprises mainly an optic-sensitive filmand a liquid-crystal film. Between them there is an opaque film and amultilayer reflector. A driving voltage is applied on these films insequence. When an optic image is projected onto the optic-sensitivefilm, it changes the resistance of the optic-sensitive film, which inturn changes the voltage falling on the liquid crystal film. Since theilluminating light first penetrates the liquid-crystal film, thenreflected by the multilayer reflector and penetrates the liquid-crystalfilm again, its phase become modulated by the optic image projected onthe optic-sensitive film. As the optic image consists of quantities ofdiscrete pixels of different intensity, different parts of the liquidcrystal film under different pixels receive different voltages and carryout different phase modulations. The liquid crystal film appearstherefore divided into quantities of discrete pixels with the same pixelsize as that of the optical image, although it is not physically dividedinto individual pixels in structure.

In FIG. 4, two identical DLPs 26 projects two optic images for phasemodulation onto the optic-sensitive films on the back of two liquidcrystal light valves 23, 24 respectively. The polarization direction ofpolarizer 7 is rotated at an angle of 45 degree with the polarizationdirection of polarizer 8 to set the liquid crystal light valves 23, 24in phase-mostly mode (different polarization direction may be requiredfor different type of liquid crystal light valves). Since two opticimages projected onto the back of two liquid crystal light valves 23, 24are in mirror symmetry with each other relative to beam splitter 9'shalf-reflect-half-transmit surface A1-A2, secondary light sources withdesired amplitudes and phases are produced by vector addition onrandom-secondary-light-source-generator-array 2. Therandom-secondary-light-source-generator-array 2 is made up with areflective scattering screen 25 covered with an opaque plate 14 bearingmicro-holes with uniform random distribution. The advantage to use aliquid crystal light valve is that more gray levels and higher displayfrequency may be obtained with the help of DLPs so as to increasestability of color display. In addition the brightness of a 3-D imagecould be greatly increased by using very high power laser.

FIG. 5 is a schematic diagram of a 3-D display device based on randomconstructive interference using twooptically-addressed-electro-optic-phase-modulators. Its opticconfiguration is the same as that in FIG. 4 except that two liquidcrystal light valves 23, 24 are now replaced by twooptic-addressed-electro-optic-phase-modulators 30, 31. In addition, thepolarizer 7, 8 are taken away. As illustrated in FIG. 6, anoptic-addressed-electro-optic-phase-modulator has similar structure as aliquid crystal light valve except that liquid crystal is replaced byelectro-optic material. It comprises the first film 35 ofoptic-sensitive material, the second film 36 of opaque material, thethird reflective film 37 and the forth film 38 of electro-opticmaterial, all of them being sandwiched between two transparentconductive glasses 34, 39 in the given order. A driving voltage V isapplied on optic-sensitive material film 35 and electro-optic materialfilm 38 via two transparent conductive glasses 34, 39. When an opticimage is projected onto the optic-sensitive film 35, it changes theresistance of the optic-sensitive film 35, which in turn changes thevoltage falling on electro-optic material film 38. As a result therefractive index of the electro-optic material film 38 changes due toelectro-optic effect. Since the illuminating light first penetrateselectro-optic material film 38, then reflected by the reflective film 37and penetrates the electro-optic material film 38 again, its phasebecomes modulated by electro-optic material film 38. The quantity ofphase modulation depends on the optic image projected on theoptic-sensitive film 35. Since the voltage V is fixed and need notchange precisely from time to time, very high voltage V could be appliedon optic-sensitive material film 35 and electro-optic material film 38to generate a phase change as large as π. To perform fast and accuratemodulation, the respond time of optic-sensitive film 35 and itsresistance relative to that of electro-optic material film 38 should beproperly designed. If another reflective film were fabricated overtransparent conductive glass 39, together with existing reflective film37, a Fabry-Perot interferometer could be constructed, which is capableof carrying out amplitude modulation. Replacing liquid crystal withelectro-optic material makes polarizer unnecessary and increases energyefficiency by twofold. In addition, 3-D display frequency might reachvery high, because the responds time of electro-optic material may reachas short as nano-seconds.

The random-secondary-light-source-generator-array in FIG. 5 is made upwith two identical opaque plates 32, 33 bearing transparent micro-holesthat are of a uniform random distribution. The plates are placed on thefront surfaces of the two optic-addressed-electro-optic-phase-modulators30, 31, that is, placed on the surface facing the projection lens 13.The opaque plate 32 is placed at an angle of 45 degree to beam splitter9's half-reflect-half-transmit surface A1-A2 and in mirror symmetry withthe opaque plate 33 relative to beam splitter 9'shalf-reflect-half-transmit surface A1-A2. Therefore their imagesprojected on transparent scattering screen 22 overlap and creates arandom coherent secondary light source array by vector addition. Theadvantage to place opaque plates 32, 33 at the object plane ofprojection lens 13 is that the magnification ratio of projection lens 13may change at any time without changing the size and the structure ofthe opaque plates. The larger the magnification ratio of projection lens13, the larger the size of obtained coherent secondary light sourcearray and the larger the possible size of displayed 3-D image. On theother hand, if opaque plates are placed at the image plane of projectionlens 13 like what happened in FIGS. 1, 3 and 4, the size and thelocation of these opaque plates have to be fixed very accurately. Whenbuilding a rear-projection 3-D TV, opaque plates may be placed at theimage plane of projection lens 13 as shown in FIGS. 1, 3 and 4. However,when magnification ratio of projection lens 13 need change constantly,it is preferable to put the opaque plates at the object plane ofprojection lens 13 as shown in FIG. 5.

FIG. 7 is a schematic diagram of a 3-D display device based on randomconstructive interference using two large-size TFT-ST liquid crystalpanels. It mainly comprises an amplitude-phase-modulator-array 1, acoherent light source 3 and an illuminating optic system 4. Theamplitude-phase-modulator-array 1 comprises the first polarizer 42; thefirst transmission liquid crystal panel 40 disposed by the firstpolarizer 42; the second polarizer 43 disposed by the first transmissionliquid crystal panel 40; the second transmission liquid crystal panel 41disposed by the second polarizer 43; and the third polarizer 44 disposedby the second transmission liquid crystal panel 41. The firsttransmission liquid crystal panel 40 and the second transmission liquidcrystal panel 41 are identical and their pixels are of a uniform randomdistribution. Therefore they play the functions of anamplitude-phase-modulator-array and arandom-secondary-light-source-generator-array at the same time. Thepolarization direction of the three polarizer 42, 43, 44 are arranged toset the first transmission liquid crystal panel 40 in phase-mostly modeand the second transmission liquid crystal panel 41 in amplitude-mostlymode. In the device illustrated in FIG. 7 this was achieved by rotatethe polarization direction of the first polarizer 42 at an angle of 45degree relative to that of the second polarizer 43 and rotate thepolarization direction of the third polarizer 44 at an angle of 90degree relative to that of the second polarizer 43. For different liquidcrystal panels different polarization directions should be chosen. Inaddition if a polarized laser beam is used, the first polarizer 42 maybe omitted. In general an illuminating optic system uses two opticlenses to expand a laser beam. To obtain a compact size the illuminatingoptic system 4 in FIG. 7 used a stack of beam splitters instead. Alongthe optic path, the reflectivity of the beam splitters increasegradually, the reflectivity of the next beam splitter being the ratio ofthe reflectivity to the transmittance of the previous beam splitter, sothat the emitted laser beams from different beam splitters are of equalintensity. The wide laser beam produced in this way penetrates the firstpolarizer 42, the first transmission liquid crystal panel 40, the secondpolarizer 43, the second transmission liquid crystal panel and the thirdpolarizer 44 in the given order, creating a secondary light source arraywith uniform random distribution. A primary 3-D image 18 may then begenerated by adjusting the amplitudes and phases of these secondarylight sources. In FIG. 7 the liquid crystal panels 40,41 may adopt avery large size, for example, as large as 19 inches or more. When 19inches liquid screen is used, the pixel pitch is about 0.29 mm anddiffraction effect becomes negligible within a short distance. The lightpassing through one pixel of the first liquid crystal panel 40 wouldincident on the corresponding pixel of the second liquid crystal panel41 without interfering with the adjacent pixels. However when the pixelpitch decreases, diffraction effect might grow and a 1:1 optic system ora micro-lens-array should be utilized to project the pixels of the firstliquid crystal panel 40 onto the second liquid crystal panel 41.

As could be seen in FIG. 7 there is an auxiliary optic element, aFresnel lens 19, placed on the right side of primary 3-D image 18. Theprimary 3-D image 18 is within one focal length of Fresnel lens 19,while the secondary light source array generated on the right surface ofthe second liquid crystal panel 41 is more than double focal lengthsaway from Fresnel lens 19. As a result a magnified virtual image of theprimary 3-D image 18 is produced on the left side of Fresnel lens 19 anda real shrunk image of secondary light source array is created on theright side of Fresnel lens 19. The separation of the final 3-D imagefrom the bright secondary light source array may greatly depress thedisturbance of the bright secondary light source array to the observerand increase the contrast of the final 3-D image.

In FIGS. 1, 3, 4 and 5, the secondary light sources are generated byvector addition. Assuming the amplitude of the illuminating laser beamfor each phase-modulator being 1 unit, the maximum amplitude of thesecondary light source generated by vector addition may reach 2 units,yielding an intensity of 4 units. While in FIG. 7 the secondary lightsources are generated by vector production. Again assuming the amplitudeof the illuminating laser beam being 1 unit, the maximum amplitude ofthe secondary light source generated by vector production may reach 1unit, yielding an intensity of 1 unit. In other words, a 3-D imagedisplayed by vector addition might be four times bright than the same3-D image displayed by vector production.

FIG. 8 is a schematic diagram of arandom-secondary-light-source-generator-array using twomicro-lens-arrays. It comprises the first micro-lens-array 45 on whichthe micro-lens are of a periodical distribution; the secondmicro-lens-array 46 on which the micro-lens are of a uniform randomdistribution disposed in parallel with the first micro-lens-array 45 andaligned with the first micro-lens-array 45 so that the focused beamcreated by each micro-lens of the first micro-lens-array 45 illuminatesone micro-lens of the second micro-lens-array 46 and the image focus ofeach micro-lens of the first micro-lens-array 45 falls within one focallength of the micro-lens of the second micro-lens-array 46. A parallellight beam incident on micro-lens-array 45 is first focused at the focusof each micro-lens of micro-lens-array 45. Next it is magnified by eachmicro-lens of micro-lens-array 46. The vertical magnification ratio isof a random distribution since the optic axis of each micro-lens ofmicro-lens-array 46 is randomly distributed relative to the optic axisof each micro-lens of the first micro-lens-array 45. The new secondarylight sources obtained is therefore of a random distribution. Themicro-lens-arrays 45 and 46 may be fabricated on the opposite sides ofthe same plate to avoid later tedious assembling work. Therandom-secondary-light-source-generator-array 2 illustrated in FIG. 8might also be used to couple two liquid crystal panels to eliminatepossible interferences of adjacent pixels due to diffraction.

FIG. 9 is a schematic diagram of arandom-secondary-light-source-generator-array 2 using a bundle ofsingle-mode fibers. It comprises a bundle of single-mode fibers 47 and amicro-lens-array 48. The single-mode fibers within the bundle 47 areoptically isolated from each other. They are glue together and polishedat the left end. A micro-lens-array 48 is disposed to focus the lightfrom illuminating optic system into the cores of the single-mode fiberswithin the bundle 47 at the left end. One micro-lens in themicro-lens-array 48 is aligned with one single-mode fiber. The lightexit from the right ends of the single-mode fibers and propagate towards3-D image 18. At the right end the spaces between adjacent single-modefibers are of a random distribution.

What is claimed is:
 1. A method for 3-D photography performed by aprocessor employing a 3-D display method based on random constructiveinterference, comprising following steps: A: Following the 3-D displaymethod based on random constructive interference, generate voxels in 3-Dspace using a coherent point light source array in which the positionsof point light sources are of a uniform random distribution; B: Read inan image from a conventional camera focused on position of the voxelsgenerated in step A; C: Repeat step A through step B so that the voxelsgenerated in step A scan through a 3-D space, meanwhile analyze theimages read in step B; record positions of the voxels as local 3-Dcoordinates of a surface when voxels' image sizes become minima;meanwhile record colors and brightness of the image as colors andbrightness of the surface of an object.
 2. The method of claim 1, wherein step C: record positions of the voxels as local 3-D coordinates of asurface when voxels' image sizes become minima; meanwhile turn off thevoxels generated in step A, read in another image from the conventionalcamera and take colors and brightness of the image as colors andbrightness of the surface of an object.
 3. A method for 3-D humanmachine interaction performed by a processor employing a 3-D displaymethod based on random constructive interference, comprising followingsteps: A: Following the 3-D display method based on random constructiveinterference, generate voxels in the air using a coherent point lightsource array in which the positions of point light sources are of auniform random distribution; said voxels form up a number of controlelements in the air. B: Read in an image from a conventional camerafocused on the position of the voxels generated in step A; C: Repeatstep A through step B, meanwhile analyze the images read in step B; whensome voxels' image sizes become minima issue a massage indicating acontrol element represented by the voxels whose image sizes becomeminima is being touched.